1. Field of the Invention
The present invention relates to compasses. More specifically, the present invention relates to electronic digital compass apparatus and methods that employ a conventional magnetic compass as a directional reference.
2. Description of the Related Art
The conventional magnetic compass was invented hundreds of years ago and has been in wide use ever since. A magnetic compass is based upon a lightweight magnet supported on a nearly frictionless pivot. In operation, the magnet aligns itself with the magnetic poles of Earth. The magnet is generally referred to as the needle of the compass, and the needle is generally enclosed in some form of housing to protect it from the environment. The movement of the needle may be damped in some fashion, such as by filling the housing with a liquid. To aid in direction finding and navigation, the compass housing is frequently marked with the traditional compass rose points, including the cardinal bearing points. The housing may include azimuth angles, referenced as 0 degrees north and incrementing in a clockwise direction through 360 degrees. In addition, a declination adjustment setting may be present to provide easy correction for the variation between magnetic north and true north. The conventional compass has several advantages including simplicity of design, low cost, familiarity to users, lack of calibration requirement, and lack of need for a power source or battery. The conventional compass also has some disadvantages. Many users find it difficult to calculate and interpret a course heading from the simple north-south pointing needle. This is particularly true in complex navigation tasks such as multiple segment courses and backtracking tasks.
Technological advancements have addressed some of the issues present in conventional compasses with the recent advent of electronic digital compasses. Digital compasses have heretofore utilized solid state magnetic sensors or integrated circuits responsive to the Earth""s magnetic fields. The outputs of such solid state sensors are coupled to a processor or controller that interprets the information and combines it with application software to drive a digital display. The display presents a magnetic heading to the user of such a device. Once the basic digital compass hardware structure of solid state sensors, a controller and a display were in place, designers then added numerous enhancements through use of software applications. For example, modern digital compasses provide features such as a programmable compass rose mode, reading and heading memory and storage, cardinal point readout in character form, declination adjustment, and heading direction indication. All of these features make the use of a digital compass more convenient than a conventional compass.
The basic trade-off between conventional compasses and digital compasses is cost. In order to acquire the advantages of a digital compass, users are required to spend more than what a conventional compass would cost. An analysis of the cost of components in a digital compass indicates that most of the components are relatively inexpensive. Microprocessors, displays, discrete circuit components, circuit boards, and the housing itself have all become rather inexpensive due to the economies of scale and the general advancements in materials and production. In fact, the sum cost of these components have dropped to very a reasonable levels. The reduction of cost of digital compasses to a level competitive with convention compasses is limited by the cost of the essential solid state magnetic sensing devices. The sensing devices remain too expensive to allow product costs to drop to the competitive level. Thus there is a need in the art for an alternative digital compass apparatus and method, which eliminates the need to employ solid state magnetic field sensing devices so as to reduce cost of the device while retaining the features and benefits that are provided through the use of all digital technology.
The need in the art is addressed by the apparatus and methods of the present invention. An apparatus for determining the orientation of Earth""s magnetic pole is taught. The apparatus includes a magnet that is pivotally coupled to a support and that is free to orient itself with Earth""s magnetic pole. It also includes a detector that is fixed relative to the support, and that has an output signal indicative of the orientation of the magnet. A display is coupled to the sensor to display an indication of the relative orientation of Earth""s magnetic pole consistent with the output signal.
In a specific embodiment of the present invention, the detector includes plural detectors positioned about the path of movement of the pivotally coupled magnet. The detector may be an optical detector. In a particular embodiment, the detector is an optical pair detector having a light emitter and a light sensor positioned to detect the orientation of the magnet. In another specific embodiment, the apparatus further includes a shutter fixed to the magnet, and the detector is an optical detector responsive to the orientation of the shutter. The optical detector may include plural optical detectors positioned about the shutter. In a refinement of the invention, the shutter has an optical pattern formed thereon and the plural optical detectors change the output signal responsive to the optical pattern. The optical pattern may include a transmissive portion and an opaque portion, or it may include a reflective portion and an absorptive portion. In one embodiment, the optical pattern is arranged with respect to the plural optical detector positions such that any single incremental change in the magnet orientation results in a change of state of the output signal caused by one of the plural optical detectors only. In a particular embodiment, the optical pattern is formed as plural arcuate portions, each concentric with the pivotal coupling, and each of the plural optical detectors lies along one of the arcs proscribed by the plural arcuate portions of the pattern.
In a particular embodiment, each of the optical sensors includes a light emitter and a light sensor positioned on opposite sides of the shutter. To improve performance, an emitter blind is positioned between the plurality of light emitters and the shutter. The emitter blind has a plurality of apertures formed therein, and each aperture is aligned with one of the plurality of light emitters. In another approach, a sensor blind is positioned between the plurality of light sensors and the shutter. The sensor blind also has a plurality of apertures formed therein, and each aperture is aligned with one of the plurality of light sensors. The light emitters may be light emitting diodes. The light sensors may be photo-diodes, photo-transistors, or light emitting diodes.
The present invention also teaches an electronic compass embodiment. The electronic compass includes a housing with a magnet pivotally coupled thereto, and that is free to orient itself with Earth""s magnetic pole. A shutter is fixed to the magnet and the shutter has an optical pattern formed thereon. The optical pattern has plural arcuate opaque portions, each concentric with the pivotal coupling, and a transmissive portion. Plural light emitters and plural light sensor are arranged as pairs and are fixed to the housing on opposite sides of the shutter. Each pair lies along one of the arcs proscribed by the plural arcuate portions. Each of the plural light sensors produces an output signal that is responsive to the optical pattern opaque portion or transmissive portion. To improve performance, an emitter blind is positioned between the plurality of light emitters and the shutter, and has a plurality of apertures formed therein. Each of the apertures is aligned with one of the plurality of light emitters. Also, a sensor blind is positioned between the plurality of light sensors and the shutter. It also has a plurality of apertures formed therein, and each aperture is aligned with one of the plurality of light sensors. A display is coupled to display an indication of the relative orientation of Earth""s magnetic pole consistent with the output signals received from the plural light sensors.
The present invention also teaches a method of determining the orientation of Earth""s magnetic pole. This method is accomplished with a device that has a housing and a magnet that is pivotally coupled thereto, a detector fixed relative to the housing, and a display. The steps of the method include orienting the magnetic poles of the magnet with Earth""s magnetic poles and detecting the orientation of the magnet with respect to the housing by the detector. Finally, displaying an indication of the relative orientation of Earth""s magnetic pole in accordance with the output of the detector.
In a specific embodiment of the method, the detector includes plural detectors positioned about the path of movement of the magnet. The detector may be an optical detector. In a refinement of the method, the device includes a shutter fixed to the magnet and the detector is an optical detector, and the detecting step is accomplished by optically detecting the orientation of the shutter. In another refinement, the shutter has an optical pattern formed thereon and the detector includes plural optical detectors. The detecting step then includes the further step of determining the orientation of the magnet by reading the output states of the plural optical sensors. The optical pattern may include a transmissive portion and an opaque portion, or it may include a reflective portion and an absorptive portion. In a specific embodiment, the optical pattern is arranged with respect to the plural optical detector positions such that any single incremental change in the magnet orientation results in a change of state in only one of the plural optical detectors. In a refinement of the method, the optical pattern is formed as plural arcuate portions, each concentric with the pivotal coupling, and each of the plural optical detectors lies along an arc proscribed by one of the plural arcuate portions. The determining step may include the step of reading the output of the plural optical sensors simultaneously or sequentially.